The present invention relates to a device for detecting the position of an optical head and, more particularly, it relates to an improvement of the device designed to detect the position of optical head which is driven linearly relative to an optical disk in the optical disk apparatus, and to direct the optical head to a predetermined track on the optical disk.
The optical disk has been developed as an information recording medium which information is optically recorded on or retrieved from. Various magnetic tapes are well known as the information magnetically-recording medium, but as compared these tapes, the optical disk can much further increase the information recording density on its recording area and provide much more stable recording condition without being influenced by any of matters such as the electric field applied from outside. Further, information is recorded on and retrieved from the optical disk by means of a light beam. Unlike a magnetic tape, the optical disk is not in contact with any other member while information is being written on it or read from it. Therefore, it is free from wearing. Furthermore, the information recorded on the optical disk can be retrieved as stable, low noise and high quality signals.
The information process apparatus provided with the optical disk needs an optical head for applying the light beam at the time of recording and retrieving information, a driver means for driving and positioning the optical head on a predetermined track on the optical head, and a device for detecting the position of the optical head relative to the optical disk.
An example of the conventional device for detecting the position of the optical head is disclosed in U.S.Pat. No. 4,607,956.
In the case of this device, a position detecting light source and a detector are opposed to each other on a fixed portion with a certain interval interposed between them, and an optical scale which moves together with the optical head is movably arranged between the light source and the detector. The optical scale has slits having a prescribed width and arranged at predetermined intervals. When the optical head is moved, the scale is also moved in the same way. As the scale is moved, the light beam applied from the light source passes through the slits, and is shut off by those portions of the scale where no slits are cut. The beam passing through each slit is detected by the detector. Hence, as the optical head is moved, the detector detects optical signals at time intervals corresponding to the intervals at which the slits are arranged. Zero signal and maximum value signal of these detected ones are counted by a counter and signals counted are processed to determine the position of the optical head and its change. In the case of this conventional device, however, the period of signals counted is determined and limited by the interval between the slits and the position detecting accuracy of the optical head cannot be therefore made higher than that allowed by the distance (or interval between the slits).